We are investigating the contributions of transcription, processing and turnover to the expression of specific genes in Drosophila cultured cells and embryos. We have evaluated these parameters in detail for the RNA transcribed from the copia sequence, a mobile DNA sequence in the Drosophila genome. In order to understand the role which the copia sequences and mobile DNA elements in general play in the cell, we are now investigating the translation product of copia RNA. In order to compare the control of expression of the copia sequence, which is expressed continuously in the cultured cells, with the control of expression of genes which are induced, we are currently measuring the parameters of synthesis, processing and turnover for two genes which are induced to a high level of expression by the stimulus of heat shock. Finally, we have demonstrated that the level of histone gene expression in Drosophila embryos is controlled both by changing rates of synthesis and by changing rates of turnover. We are currently investigating different mechanisms by which the control of histone mRNA turnover might be controlled.